This application claims the priority of German application No. 100 13 437.8-44, filed Mar. 17, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a foil for an evaporator, in particular a double evaporator, composed of foils for converting a liquid media mass flow into a gaseous media mass flow.
A single evaporator composed of foils is disclosed in DE 44 26 692 C1. The two-stage evaporator unit converts a liquid reactant mass flow, which can be set as a function of a predetermined load, into a gaseous reactant mass flow. The liquid reactant mass flow is at least partly evaporated by a heat-transfer medium in a first stage, and is completely evaporated, if need be, in a second stage and then is superheated. In this case, it is proposed that the evaporator unit be formed by alternately stacking, one on top of the other, foils having heat-transfer channels and foils having reaction channels. In each case, at least a first stage and a second stage are integrated in a foil, the first stage being designed as a channel having a minimized cross-sectional area so as to directly adjoin an inflow line. The first stage is operated at high heat-transfer coefficients, and the overall cross section of the reaction channels increase in the second stage in the direction of flow.
In evaporators of such construction, the evaporated reactant mass flow will normally discharge from each of the reaction or media foils into a common collecting space in the discharge region and the gaseous reactant mass flow is drawn off via a discharge line. In this case, intermixing of the reactant mass flows flowing out of the respective reaction foils can occur in the collecting space arranged in the discharge region, so that there is a comparatively uniformly evaporated reactant mass flow at the outlet.
Nonetheless, such an evaporator unit has the disadvantage that it is not possible to reliably determine that region of the channels, made in the foil, in which the actual evaporation takes place. As a result, a uniform distribution of the reactant mass flow to be evaporated in each of the foils is adversely affected. Although this disadvantage can be partly removed by the above-described mixing in the collecting space, it would be desirable, for the efficiency and for the best possible power transmission in the evaporator unit, to obtain a uniform distribution in each of the foils. Reactant mass flows which are heated or evaporated in a very uneven manner are already superheated in sections of the evaporator, in which case there will still be liquid droplets in the reactant mass flow in other sections and possibly also in the outlet region. In the worst case, xe2x80x9ccold channelsxe2x80x9d, through which comparatively cold, possibly even liquid, portions of the reactant mass flow will pass through the evaporator unit, may therefore form.
The object of the present invention is to achieve an ideal and uniform distribution of the medium to be evaporated and of the evaporated medium, in particular in the discharge region of the foils of an evaporator composed of foils.
According to the present invention, because the pressure gradient in the medium is markedly smaller than the pressure gradient over the length of the media foil through which flow occurs, a very uniform distribution of the evaporated medium in the discharge region is achieved. Ultimately, this is also assisted in an especially advantageous manner by virtue of the fact that the discharge region can be heated.
Due to the uniform distribution of the medium over the entire area, in particular over the entire width of the discharge regionxe2x80x94the uniform distribution being achieved by the considerably smaller pressure gradient there than the pressure gradient over the length through which flow occursxe2x80x94it can be ensured that the medium in the discharge region is distributed very uniformly, and that no dead zones are produced in which there is no media flow or only a very slight media flow. A uniform flow and thus uniform utilization of the available energy also take place in that region of the media flow which is arranged directly upstream of the discharge region in the direction of flow, since xe2x80x9cdammingxe2x80x9d in the region of the media foil cannot occur as a result of stationary medium collecting in the discharge region.
In addition, the discharge region is arranged in the heated area of the media foils, so that the discharge region performs more than the pure function of a collecting space, and the gaseous media portions, discharging over the width of the respective media foil, can be intermixed in the heated discharge region. Thus a very uniform distribution of the medium evaporating in the respective foil occurs before this medium leaves the foil to go into a collecting space, which then connects a plurality of such foils and a discharge line to one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.